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Topic: Got a technical question? (Read 1783 times)

I joined to use the classifieds, so I thought I would try to make myself usefull.I have read a great deal about glass over the years, including every fusion magasine (The American Scientific Glassblowers Society journal) from June of 1956 to November of 2002 inclusive. While my focus has been learning about borosilicate, I might have an answer for your oddball question.

A low coefficient of expansion (C.O.E.) makes borosilicate less prone to heat stress. Soda-lime glasses tend to crack much more easily in the flame, but they allow for a much larger colour selection, as it is worked at a lower temperature.

Assuming you are looking at a finished piece, and not at raw material you can do compatibility test with in the flame, the simplest way to distinguish between hard and soft glass is by density. Soft glass weighs 1/3 more, or hard glass weighs 1/4 less, depending on which one is considered normal. Simplest way in the flame is to take a small piece of a known glass, and an equal piece of the unknown glass, and make a blob with them overlapping. Pull this out into a thread, and watch how much it curves as it cools.

Cobalt blue has been around in limited quantities for quite some time, but generally speaking, early to mid 90's was when borosilicate colours became available. I was mixing my own colours when I started back in '93.

Yes, those look like soft glass colours to my eye, even ignoring the dates. No reduction of the transparent greens (in boro, copper dioxide transforms to copper oxide on the surface unless silly amounts of oxygen are used, giving it a reddish skin or streaks). The opaque yellows and oranges (cadmium) have only become available in boro in the past few years, and are prone to boiling.

That is extrermely useful as the popularity of lampwork figures is growing and this will make it easier to separate the older from some of the new. Won't help where soda lime glass is used but it does at least help in dating etcetera.